Polyacetal resin is widely used in a variety of fields such as in the field of automobile parts, etc., because of its excellent mechanical strength, abrasion resistance, creep properties, fatigue properties and electrical properties.
In general, however, polyacetal resin has a problem in that surface decorating such as printing, coating, etc., is difficult due to its poor surface activity. Therefore, several attempts have been made to improve its surface decorating performance. For example, there has been proposed a method of preliminary treatment with acidic chemicals of phosphoric acid and sulfuric acid, a method of using a cellulose-based coating composition as a primer, a method of using a primer prepared by dissolving a chlorinated polyolefin resin in a chlorine-containing solvent, and some other methods have been proposed to improve surface decorating performance.
However, these methods are not fully satisfactory due to problems such as the requirement of additional processing steps for acid treatment and washing with water, deformation of the material due to a step of drying the coating, harmfulness of a chlorine-containing solvent, etc.
An object of this invention is to overcome the above problems associated with the prior methods such as the requirement of additional processing steps, deformation of the material, harmfulness of a chlorine-containing solvent, etc. That is, the present invention seeks to simplify a coating step and to reduce production costs so that a decorative article having a coating with high bond strength can be produced free from material deformation by only applying a coating composition directly to a polyacetal molded article surface without any chemical treatment or primer treatment and drying the coating.
An acetal polymer is usually produced by homopolymerization of formaldehyde or trioxane, or by copolymerization of formaldehyde or trioxane with a cyclic ether.
For example, U.S. Pat. No. 3,218,295 discloses the Polymerization of formaldehyde in the presence of a polyalkylene glycol or a vinyl compound such as a vinyloxyethylamine/methyl methacrylate copolymer or a vinyloxyethylamine/isobutyl methacrylate copolymer. U.S. Pat. No. 3,732,333 also discloses the polymerization of formaldehyde in the presence of a living polymer of a vinyl compound such as styrene or methyl methacrylate.
However, polymers obtained by the above polymerization processes can hardly give the surface decorating performance referred to in the present invention. Further, the mechanical properties inherently belonging to a polyacetal resin are degraded to a great extent.
The polymer of the above U.S. Pat. No. 3,732,333 also has a defect in that the polymer is a mixture of a vinyl polymer with an aldehyde homopolymer due to its polymerization process in which formaldehyde is polymerized in the presence of a living polymer as a polymerization initiator.